1. Field of the Invention
Embodiments of the present invention generally relate to the fabrication of integrated circuits. More specifically, embodiments of the present invention generally relate to processes for depositing a layer on a substrate and then annealing the substrate.
2. Description of the Related Art
Many processes in integrated circuit fabrication require rapid high temperature processing steps for deposition of layers on semiconductor substrates, such as silicon-containing substrates, or annealing of previously deposited layers on semiconductor substrates. For example, after dopant ions, such as boron, phosphorus, or arsenic, are implanted into a semiconductor substrate, the substrate is typically annealed to repair the crystalline structure of the substrate that was disrupted during the doping process and to activate the dopants.
It is typically preferred to heat and cool substrates quickly to minimize the amount of time that a substrate is exposed to high temperatures that can cause unwanted diffusion. Rapid Thermal Processing (RTP) chambers and methods that can raise substrate temperatures at rates on the order of about 200 to 400° C./second have been developed. RTP processes provide an improved rapid heating method compared to the heating provided by batch furnaces, which typically raise substrate temperatures at a rate of about 5-15° C./minute.
While RTP processes can heat and cool a substrate quickly, RTP processes often heat the entire thickness of a substrate. Heating the entire thickness of a semiconductor substrate is often unnecessary and undesirable, as the devices requiring annealing on a semiconductor substrate typically only extend through a top surface layer, such as a few microns of the substrate. Furthermore, heating the entire thickness of the substrate increases the amount of time required for the substrate to cool down, which can increase the time required to process a substrate and thus reduce substrate throughput in a semiconductor processing system. Increasing the amount of time required for the substrate to cool down also limits the amount of time the substrate can be exposed to the elevated temperature required for activation. Shorter heating and cooling times are also desirable because they limit diffusion and minimize device shrinkage.
Uneven heating across the surface of a substrate is another problem that is often experienced with RTP or other conventional substrate heating processes. As today's integrated circuits generally include a plurality of devices spaced at varying densities across a surface of a substrate and having different sizes, shapes, and materials, a substrate surface can have very different thermal absorption properties across different areas of the substrate surface. For example, a first region of a substrate having a lower density of devices thereon typically will be heated faster than a second region of the substrate that has a higher density of devices thereon than the first region. Varying reflectivities across different areas of the substrate surface can also make uniform heating of the substrate surface challenging.
Therefore, there remains a need for a method of uniformly heating a semiconductor substrate across a surface of the substrate during an annealing process.